The aim of this research was finding the influence of anatomy-based and functional-based outflow boundary conditions for computational fluid dynamics (CFD) on fractional flow reserve (FFR) and wall shear stress (WSS) in mildly diseased coronary bifurcations. For ten patient-specific bifurcations three simulations were set up with different outflow conditions, while the inflow was kept constant.
First, the outflow conditions were based on the diameter of the outlets. Second, they were based on the volume estimates of the myocardium that depended on the outlets. Third, they were based on a myocardial flow measure derived from computed tomography perfusion imaging (CTP).
The difference in outflow ratio between the perfusion-based and the diameter-based approach was -7 p.p. [-14 p.p.: 7 p.p.] (median percentage point and interquartiles), and between the perfusion-based and volume-based this was -2 p.p. [-2 p.p.: 1 p.p.]. Despite of these differences the computed FFRs matched very well. A quantitative analysis of the WSS results showed very high correlations between the methods with an r2 ranging from 0.90 to 1.00. But despite the high correlations the diameter-based and volume-based approach generally underestimated the WSS compared to the perfusion-based approach.
These differences disappeared after normalization. We demonstrated the potential of CTP for setting patient-specific boundary conditions for atherosclerotic coronary bifurcations. FFR and normalized WSS were unaffected by the variations in outflow ratios. In order to compute absolute WSS a functional measure to set the outflow ratio might be of added value in this type of vessels.

A.F.W. van der Steen (Ton) , F.J.H. Gijsen (Frank)
Erasmus University Rotterdam
Financial support by the Dutch Heart Foundation for the publication of this thesis is gratefully acknowledged. Additional financial support for the printing of this thesis was kindly provided by Cardialysis and Pie Medical Imaging.
Erasmus MC: University Medical Center Rotterdam

Schrauwen, J.T.C. (2016, February 19). Wall Shear Stress in Coronary Arteries. Erasmus University Rotterdam. Retrieved from